iOS please help (removing image to reveal one underneath)

[tomcat77]

i am trying to code an app but having a hard time doing one element of it:

i want to make use of the touch screen and only erase the upper layer of an image and reveal the image underneath as the user touches the screen. similar to the isteam application. can someone please tell me how to do this?

id really appreciate it

thank you

hello

i will really appreciate some help on this matter. please advise.

thanks